Gaseous discharge lamp



March 9, 1943. R. N. THAYER GASEOUS DISCHARGE LAMP Filed March 28, 1941 Edward N. Thager, b W His Af't'OT'nH Inveni'or:

Patented 951943 UNITED STATES PATENT OFFICE Gaseous 35m ns 1 I Richard N. Thayer, Cleveland Heights, Ohio, as-

signortoGeneralElectrloOom ration of New York n w, I rpo- Application March 28, 1941, Serial No. 385,661

My invention relates to gaseous discharge lamps having preheated thermionic cathodes, for example, those lamps of the fluorescent type shown and described in the U. 8. Patent No.

2,182,732 to Meyer et a1. More particularly the invention relates to an improved means for preheating the cathodes and for initiating the discharge after such preheating. The invention consistsjin the new and novel. arrangement of elements hereinafter disclosed and claimed.

In most gaseous discharge lamps of the aforesaid type. it has generally been necessary to provide means for passing a preliminary heating current through the cathodes and for subsequently automatically discontinuing said preliminary current and simultaneously initiating the main discharge when the cathodes have reached emitting temperature. This requirement arises from the fact that the-cathodes are subiect to damaging positive ion bombardment if the current is drawn from them before they begin to emit electrons in substantial quantities. In most commercially successful arrangements the problem is solved by passing current through ,the cathodes in series and 'by providing temperature or current responsive means to break the series connection when the desired cathode temperature is reached. Many such arrangements have been devised but all have been subject tosome objectionable featuresmuch as high cost, complexity, bulkiness, relatively short useful life, and/or improper cathode heating. By my improved construction, I have provided a simple and effective :lamp starting meansof this I type which avoids many of these objections and which permits the incorporation of the discharge producing members and the 1starting means within a singleenvelop'e'.

12 Claim .(Ci- 176-122) It is accordingly an object of my invention to provide a new and improved starting means for discharge lamps, which means shall be simple in construction and economical in manufacture.

It is a further object of the invention to provide a new and improved discharge ,lamp in which the starting means may be incorporated directly within the lamp and which shall depend directly upon the cathode. temperature for operation.

It is still a further object of the invention to provide 'a new and improved thermostatically operated unit for automatically discontinuing the cathode preheating operation in lamps of the aforesaid type and thereafter automatically initiating the discharge.

Further objects "and advantages of the invention will be apparent from the following detailed description thereof and from the accompanyingdrawing in which the Fig. 1 shows a lamp constructed in accordance with the invention along with a circuit for operating the same. while Fig. 2 shows in perspective and in greater detail the improved starting and cathode unit. The Fig. 3 shows schematically the geometrical configuration oi the bimetallic switching unit, while the Fig- 4 shows an atlernatlve modifica- I tion of the lamp shown in Fig. 1. Corresponding mounted therein a pair of thermionic cathodes Generally the objects of the inven- 7 tion are accomplished by providing a bimetallic member adjacent to the cathode and arranged to operate a pair of contacts which controlthe series preheating circuit. control willinsure that during the starting operation the cathode is neither too cold, which would cause its rapid destruction by positive ion bombardment, nor too hot, which would foster rapid evaporation. By my-construction it is possible .to approach this ideal preheatinggcontrol much moreclcsely because the controlling elements are responsive to cathode temperature itseli'rather than to the temperature of the lamp as a whole or to completely independent conditions as is the case with many of the arrangements now common in the art.

The ideal preheating ll and 12 of the conventional coiled type, as

well as a filling of mercury vapor which may be providedby a'globule oi'mercury it. A starting gas such as one of the rare gases at pressures up to several may also be provided in the usual manner. The cathode i2 is also provided with a pair of auxiliary electrodes it one of which is attached to each end thereof. These serve as the anodes of the lamp dllring'that portion of the cycle in which the cathode i2 is at higher potential than cathode Ii. The cathode Ii is provided with but one auxiliary anode ll, while in place. of the other is substituted the coiled bimetallic strip ll mounted on an exten-. sion ll of the cathode lead wire. As shown, the bimetallic strip ii is in close proximity to the cathode Ii and is attached at its free end to a )1 sliding plunger or contact 18. The plunger i6 is arranged to slide in the open end of capillary tube II, which biased to the stem press It of e lamp and mounted co-axially with the lamp. At the lower or closed end of the capillary i1 is positioned a second and preferably xed contact I curvature.

i9 which is arranged to make contact with the 2,313,683 construction consequently simplified. In this case, the lamp is shown as a single ended lamp having the cathodes ii and II as in Fig. l, the cathode l2 being supported by the members 33 which may be ceramic or glass tubes enclosing the leads-thereto. The lead 34 enclosed in left hand tube 33 and corresponding to the lead 30 .01 Fig. 1 will interconnect the cathodes II and heating the cathode ll during the process of- 3 for the reason that, for a given length of 111- metal, this form permits the closest spacing oi the strip to the cathode. It will be understood that it is desirable to space the bimetal as closely as possible to the cathode without destroying its temper by excessive heating in order that it will follow as closely and as quickly as possible the temperature variations thereof. If it is spaced too far from the cathode, it will tend to follow the temperature variations .of the walls rather than those of the cathode. The bimetallic strip l5 should be oriented so that'it draws contact it from the capillary tube without binding. I have found that this can be accomplished by so positioning the strip that the chord or diameter subpanys No. 2400 bimetal having the dimensions .20 mm. by 2 mm. and being 6 mils thick. It was bent into the form of a semicircle of 12.5 mm.

diameter having the cathode at the center of I The capillary. Ilv was formed. of a glass tube having an internal diameter from 40 I! in a manner similar to that of Fig. l. The insulating members 33 maybe fused or cemented to the stem press, as shown at 35. The base 36 which maybe of the conventional type is provided for the termination of the various leads. It will also be understood that the lead 30 of'Fig. 1 may also be placed within the lamp shown in that figure. If that is done, only a single contact on the bases 32 and 31 will be necessary.

The operation of the lamp shown in Fig. 1 will be as follows. In the unheated condition of the. lamp, the bimetallic strip I5 is so positioned as to force the plunger l6 and the contact I! into contact with each other. When the switch 28 is closed, heating current of suitable magnitude determined by the overall impedance of the circuit will pass through the circuit comprising the choke coil 28, the lower lead 20, the cathode ii,

the bimetallic strip IS, the contacts Mend it, lead 30, the cathode i2, and the lower lead 25. When the cathode Ii has become sufllciently heated by this current, the bimetallic strip it to start the discharge between the cathodes H and I! will be developed by the inductance of the circuit. Thereafter, the bimetallic strip will bermaintained in the open position by the heat from the-cathode, as well as by the heating effect of the are for which it serves as an anode during the hall cycle in which it is positive with respect to cathode I2. I

Hitherto, devices of this type have been unsuccessful because the arc fromthc cathode Ii tends to strike at the contact l9 rather than at the cathode I2. The difllculty has been solved hitherto by enclosingthe contacts. corresponding to 45 mils, the sliding contact l6 having a diameter of from 25 to 35 mils. The pressure exerted between the two contacts when the bimetallic strip was at room temperature was adjusted to be from 40 to 50 grams. The capillary projected from 3 to 4 millimeters above the end of the fixed contact IS. with these dimensionsit was found that the contacts would open in from 4 to 6 seconds after a line voltage of about 118 volts was applied to the lamp. It will be understood.

' of course, that all of these dimensions will be somewhat changed for lamps of diilerent wattage. For example, in the case of the lower wattage lamps the cathodes will have a smaller heat capacity, and consequently the heating time will be much shorter.

For the purpose of energizing the lamp, any suitable source of electrical energy may be provided, such as the alternating current source'il to l8 and IS in a vacuum chamber within the main discharge chamber. -This expedient,.however, is not only costly but it also slows up the operation of the device because of the poor heat exchange between the bimetallic strip and the surrounding discharge members through the vacuum. In my construction, however, the arc is prevented from centering on the contact I! by the capillarytube l1 and also by the fact that the plunger l6 partially closes the opening of the mechanism could withstand well over 15.000 in-' dividual starts. At the same time, the overall starting time of the lamp from the cold condition could be made less than 2 seconds. It will be apparent from this and from what has alrea y been said above that I have'provided a construction that is eilective in operation and relatively simple and economical in manufacture.

It will be understood that in the foregoing I have described but one of the many possible embodiinents or my invention. and that many variationsinthestructural'detailsmayoccurtothose ae aees skilled in the art to which it appertains. Forexample, many modifications in theshape. size, and position of both capillary member I! and the bimetallic strip l may be made without departing from the true spirit and scope of the invention. All such modifications I aim to include within the scope of the appended claims.

ceiving relation to one of said electrodes, said switch comprising a chamber. of insulating material open to said space, a contact in said chamber and insulated from said discharge space by the walls thereof, a second contact partially closing the opening .of said chamber, a bimetallic member exposed directly to heat from said electrode and fixed at one of its ends and connected to from said discharge space by the walls thereof,

a second contact partially closing the opening or said chamber a bimetallicmember exposed di- 'rectly to heat from said electrode and fixed at one of its ends and connected to one of said contacts at the other, whereby said ontacts are separated by expansion of said bimetallic member;

and means for forming a preheating circuit through said electrode by closure of said contacts. '2. A gaseous discharge device comprising a sealed envelope having a discharge space, a gaseous atmosphere therein, at least one therm-,

ionic electrode adapted to be heated to emission temperature therein, a bimetallic switch mounted within said envelope and in heat receiving relation to said electrode, said switch comprising a chamber of insulating material open to said space, a fixed contact in said chamber and in.-

sulated from said discharge space by the walls thereof, a movable contact partially closing the opening oi said chamber, a bimetallic member exposed directly to heat from said electrode and connected'at one of its ends to said electrode and' heated to emission temperature, a bimetallic switch mounted within said envelope and in heat receiving relation to said electrode, said switch comprising a tubular member of insulating material afiixed.at one end to said stem press and open to said space at the other end, a stationary contact in said tubular member and insulated from said discharge space by the walls thereof, a movable contact partially closing the opening of said tubular member and slidable therein, a bione'of said contacts at the other, whereby said contacts may be separated by expansion of. said bimetallic member, said bimetallic member being adapted to be heated by an arc discharge between said electrodes and said contacts and thereby held in open position; and means for forming a preheating circuit through said electrodes and said contacts in series.

5. In combination, a gaseous discharge lamp comprising a sealed envelope having a discharge space and a gaseous atmosphere therein, a pair of thermionic electrodes adapted tobe heated to emission temperature therein, a bimetallic switch mounted within said envelope and in heat receiving relation to one of said electrodes, said switch comprising a chamber of insulating material open to said space, a contact in said chamber and insulated from said discharge space by the walls thereof, a second contact partially closing the opening of said chamber, a bimetallic member exposed directly to heat from said electrode and fixed at one of its ends and'connecte'd to one of said contacts at the other, whereby said contacts may be separated by expansion of said himetallic member, said bimetallic member being adapted to be heated by an arc discharge between said electrode and said contacts and thereby held in open position; and means wholly within said envelope for forming a preheating circuit through said electrodes and said contacts in series.

6. In combination, a gaseous discharge lamp comprising a sealed envelope having a discharge space and a gaseous atmosphere therein, a pair 01 thermionic electrodes each mounted in a stem press and adapted to be heated to emission temperature therein, a bimetallic switch mounted within said envelope and in heat receiving relation to one of said electrodes, said switch comprising a tubular member of insulating material amxed at one end to said stem press and open to said discharge space at the other, a fixed contact member surrounding said one of said electrodes in direct heat receiving relation thereto and electrlcally connected at one of its ends to said one metallic member surrounding said electrode in direct heat receiving relation thereto and conof said electrodes and to said movable contact at the other, whereby said contacts may be separated by expansion ofsaid bimetallic member, said bimetallic member being adapted to be heated by an arc discharge between the said electrodes and said contacts thereby held in open position; and means for forming a preheating cirnected at one of its ends to said electrode and to said'movable contact at the other, whereby said contacts may be separated by expansion of said 7 minating therewithin, a co-op'erating movable contact fitting comparatively snugly in-s'aid bore and arranged to slide longitudinally therein, and

and'a thermal switch responsive to heat from said electrode, said switch comprising a member having a comparatively small bore therein communicating with the interior of said envelope through one end and closed at its other end, a fixed contact projecting into said bore through its closed end and terminating therewithin, a cooperating movable contact fitting comparatively 1 snugly in said bore and arranged to slide longitudinally therein, and a thermally responsive ele-- ment located adjacent to said electrode and responsive to heat emitted therefrom, said thermala,sis,oss

across said second lead-in conductor and said support wire, and a bimetallic element mounted at one end on said support wire and secured at its opposite end to said movable switch contact, said ii. In an electric discharge device comprising a sealed envelope, an electrode and switch assembly within said envelope comprising a thermionic cathode, a bimetallic switch element located adjacent to said cathode, a stationary switch conhr responsive element being connected to said movable contact to move it into and out of engagement with said fixed contact.

9. In an electric discharge device comprising a sealed envelope, an electrode and switch assembly comprising a stem of vitreous material having an integral tubular projection thereon with a comparatively small bore closed at the end adjacent said stem but open to the interior or said envelope at its opposite end, a conductor sealed through said stem and projecting into the bore of said projection through its closed end and terminating therewithin to form a fixed contact, a co-v operating movable contact fitting comparatively snugly in said bore and arranged to slide longitudlnally therein, a thermionic electrode carried I by said stem, and a. thermally responsive element carried by said stem adjacent to said electrode and responsive to heat emitted therefrom, said thermally responsive element being connected to said movable contact to move it into and out of engagement with said fixed contact.

10. In an electric discharge device comprising a sealed envelope, an electrode and switch assembly comprising a stem oi-vitreous material having an integral tubular projection thereon with a comparatively small bore closed at the end adjacent said stem but open to the interior of said envelope at its opposite end, a current lead-in conductor sealed through said stem and projecting into the bore of said projection through its closed end and terminating therewithin to form a fixed contact, a co-operating movable contact fit-' ting comparatively snugly in said bore and arranged to slide longitudinally therein, a second tact, a cooperating movable switch contact secured to the movable end of said bimetallic element and normally engaging said stationary contact but separable therefrom upon heating of the bimetallic element by said cathode, a support wire carrying and electrically connected to one end of said cathode and to the fixed end 0! said bimetallic element, a current lead-in conductor connected to the other end of said cathode, a second current lead-in conductor electrically connected to said stationary contact, and an auxiliary anode electrically connected to said firstmentioned lead-in conductor.

12. In an electric discharge device comprising a sealed envelope, a pair of c'o-operating electrodes in said envelope at least one of which is a thermionic electrode, apreheating circuit-for said thermionic electrode including a thermal switch comprising-a bimetallic element and normally closed fixed and movablecontacts, said bimetallic element being exposed to the atmosphere in said envelope in direct heat receiving relation to said thermionic electrode and being electrically connected at its fixed end to one end of said thermionic electrode, saidmovable contact being carried by the movable end 0! said bimetallic element, means for connecting said fixed contact to the co-operating electrode to shunt the dissaid movable contact fitting comparatively snuglv insaid bore to prevent striking 01' a discharge from said thermionic electrode to said fixed con- 1 tact when said contacts are in open position.

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